It's called "cosmoline" and it is a rust inhibitor. Most manufacturers spray untreated metal with it to prevent corrosion. I bought a spectra and it had cosmoline on it. I chose to leave the tank the OEM color which was a metal finish, cleaned off the cosmoline and sprayed with a Eastwood cosmoline type to prevent corrosion. If it has this stuff on the inside, I'm sure it'll be just minimal and your first fill up will flush it out. The 2 filters (tank and carb) will catch anything you don't want in the carb.